1. Field of the Invention
The present invention relates generally to optical communication systems and, more particularly, to micro-electro-mechanical optical devices.
2. Description of the Related Art
Optical communication systems typically include a variety of optical devices (e. g., light sources, photodetectors, switches, attenuators, mirrors, amplifiers, and filters). The optical devices transmit optical signals in the optical communications systems. Some optical devices are coupled to electro-mechanical structures (e. g., thermal actuators) forming an electro-mechanical optical device. The term electro-mechanical structure as used in this disclosure refers to a structure which moves mechanically under the control of an electrical signal.
Some electro-mechanical structures move the optical devices from a predetermined first position to a predetermined second position. Cowan, William D., et al., "Vertical Thermal Actuators for Micro-Opto-Electro-Mechanical Systems", SPIE, Vol. 3226, pp. 137-146 (1997), describes one such electro-mechanical structure useful for moving optical devices from predetermined first positions to predetermined second positions.
In Cowan et al., the electro-mechanical structure is a thermal actuator. The thermal actuator is coupled to an optical mirror. Both the thermal actuator and the optical mirror are disposed on a surface of a substrate. The thermal actuator has two beams. A first end of each beam is coupled to the optical mirror. A second end of each beam is attached to the substrate surface.
Each beam of the thermal actuator has two material layers stacked one upon the other. The stacked material layers each have a different coefficient of thermal expansion, with the topmost material layer of each beam having a coefficient of thermal expansion larger than that of the other material layer.
The thermal actuator mechanically moves the optical mirror in response to an electrical signal being applied to the beams. Applying the electrical signal to the beams heats the stacked material layers. Thereafter, upon removal of the electrical signal, the stacked material layers cool. Since the topmost layer of each beam has the larger coefficient of thermal expansion, it contracts faster than the underlying material layer when cooled. As the topmost material layer contracts, it lifts the first end of each beam as well as the optical mirror coupled thereto a predetermined height above the plane of the substrate surface. Additional heating and cooling of the beams does not change the height of the optical device with respect to the plane of the substrate surface. As such, the usefulness of thermal actuators is limited to one-time setup or positioning applications.
Thus, electro-mechanical structures suitable for controlling the movement of optical devices continue to be sought.